How to Fix a Drafty Window
Updated September 18, 2026
Can I do this myself?
Safe to DIY
Yes, sealing drafts is safe and easy from indoors. Take care on ladders for outside caulking, avoid open flames when hunting for leaks, and test old paint for lead before scraping window frames.
A drafty window lets in cold air in winter, hot air in summer, and dust, noise and insects all year. It makes rooms uncomfortable near the window and forces heating and cooling to work harder. The leak is usually in one of three places: between the moving sash and the frame, between the frame and the wall, or around the glass itself.
Finding the exact spot is the key to a good fix. You don’t need special equipment, and you should avoid the old trick of holding a candle or incense stick near the window: open flames near curtains and blinds are a real fire risk. A damp hand, a thin strip of tissue, or an inexpensive thermal leak detector works just as well.
Once you know where air is coming in, the fixes are simple: weatherstripping for gaps where the window opens, caulk for cracks around the fixed frame, and temporary options like rope caulk or insulating window film for the coldest months. None of them needs professional skills.
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Signs of the problem
- You can feel moving air near the window on a windy or cold day
- Curtains or blinds move slightly when the window is closed
- Dust or grit collects on the sill even when the window stays shut
- Visible gaps or daylight around the sash or frame
- Cracked, shrunken or missing caulk on the outside of the frame
- Condensation, frost or cold spots on one part of the frame
Common causes
Worn or missing weatherstripping
Most commonOpening windows use foam, rubber, felt or brush strips to seal the moving parts. Over years they compress, crack or fall off, leaving gaps where the sash meets the frame. This is the most common cause of drafts.
Failed caulk around the frame
Most commonCaulk seals the joint between the window frame and the wall, inside and out. Sun, heat and building movement make it shrink, crack and pull away, letting air and sometimes water in.
Sash not closing tightly
SometimesA loose or broken lock, bent hardware or a swollen sash can stop the window from pulling closed against its seals. Sliding windows can also leave a gap where the two panels meet.
Loose glazing or single-pane glass
SometimesOn older windows, the glazing putty holding the glass can crack and fall out, letting air leak around the glass. Single-pane glass also feels cold and creates a draft by chilling the air next to it, even with no actual leak.
Rotted or damaged frame
Less commonWooden frames that stay wet can rot, shrink and warp, opening gaps that can’t be sealed well. Soft, crumbling wood is a sign the frame needs repair or replacement.
Safety first: before you start
- Critical:Don’t use candles, lighters or incense to find drafts. Curtains, blinds and dust near windows catch fire easily. Use a damp hand, tissue strip or a thermal leak detector instead.
- Critical:For exterior caulking above ground level, use a stable ladder on firm, level ground, keep three points of contact, and don’t overreach. Leave upper-storey work to a professional if you’re not comfortable.
- In homes built before about 1980, test window paint and old putty for lead before scraping or sanding. Old glazing putty and caulk can also contain asbestos.
- Wear safety glasses when scraping old caulk and gloves when using solvent cleaners.
- Ventilate the room when using caulk or adhesive, and keep solvent-based products away from heaters.
Tools & materials
Tools
- Thermal leak detector (optional) or strips of tissue paper
- Utility knife and plastic scraper
- Caulking gun
- Scissors and tape measure
- Hair dryer (for window film)
- Safety glasses and gloves
Materials
- Self-adhesive weatherstripping (foam, rubber V-strip or brush pile to suit the gap)
- Exterior-grade silicone or polyurethane caulk; paintable acrylic caulk for interior trim
- Rope caulk (removable sealing putty)
- Insulating window film kit
- Rubbing alcohol or mild detergent for cleaning surfaces
Step-by-step fix
- 1
Find the leaks without a flame
Choose a windy or cold day. Close the window, turn off fans, and move a damp hand slowly around the sash, frame edges, and the joint between frame and wall; leaks feel noticeably cool. A strip of tissue held between your fingers will flutter at a leak. A thermal leak detector shows cold spots as a colour change.
Tip: Another test: close the window on a strip of paper. If it slides out easily, the seal at that point is weak.
- 2
Check the lock and fit
Close and lock the window firmly. If the lock doesn’t pull the sash tight, tighten its screws or adjust the keeper. Sometimes a properly tightened lock is enough to close the draft.
- 3
Remove old weatherstripping
Peel off damaged weatherstrip and scrape off leftover adhesive with a plastic scraper. Clean the surface with rubbing alcohol or mild soapy water and let it dry completely; new adhesive won’t stick to dust or grease.
- 4
Fit new weatherstripping
Measure the gap and pick the right type: foam tape for small, even gaps on surfaces that press together; rubber V-strip or tubular gaskets for larger or uneven gaps; brush pile for sliding windows. Cut to length and press it firmly in place, making sure the window still closes and locks.
Tip: Too thick a strip stops the window closing properly. If the lock becomes hard to turn, use a thinner profile.
- 5
Recaulk gaps around the frame
Where air leaks between the frame and the wall, cut out cracked caulk with a utility knife and clean the joint. On dry days above about 5 °C (40 °F), run a steady bead of exterior-grade caulk along the gap outside, and paintable acrylic caulk inside, then smooth it with a wet finger or tool. Don’t caulk over weep holes at the bottom of the frame; they drain water.
Warning: Use a stable ladder for exterior work and never overreach. For upper floors without safe access, leave outside caulking to a professional.
- 6
Use rope caulk for windows you won’t open
For the coldest months, press rope caulk into the gaps around a window you don’t plan to open. It’s pliable, fills irregular gaps, and peels off cleanly in spring without damaging paint.
- 7
Add insulating window film
For old or single-pane windows, a clear shrink film kit adds a layer of still air. Clean the frame, apply the double-sided tape around the inside of the frame, stretch the film over it, then shrink it tight with a hair dryer on a warm setting until wrinkles disappear.
- 8
Retest
Repeat the damp-hand or tissue test on another windy day. Treat any remaining leaks and check that the window still opens, closes and locks properly.
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How to check it's fixed
- No noticeable air movement around the closed window on a windy day
- The window closes, locks and opens smoothly with the new seals
- Caulk forms a continuous, well-bonded bead with no gaps
- Less dust on the sill and no fluttering curtains
When to stop and call a professional
- The frame is soft, rotten or crumbling
- Water leaks in around the window during rain, or stains appear on the wall below
- Double-glazed units are fogged or have moisture between the panes
- Exterior work needs a ladder above the first floor or scaffolding
- Old paint or putty tests positive for lead, or you suspect asbestos in the putty or caulk
How to prevent it
- Inspect weatherstripping and caulk every year before winter or the rainy season.
- Keep weep holes and window tracks clean so water can drain.
- Repaint wooden frames when paint starts to crack to protect the wood.
- Close windows fully and use the locks, which keep the seals compressed.
Frequently asked questions
How do I find where a window draft is coming from?
On a cold or windy day, move a damp hand slowly around the frame and sash, or hold a strip of tissue and watch for it to flutter. A thermal leak detector points out cold spots quickly. Avoid candles or incense near curtains.
Should I use weatherstripping or caulk?
Weatherstripping for joints that move, such as where the sash meets the frame. Caulk for joints that never move, such as between the frame and the wall. Most drafty windows benefit from both.
Can I seal a window from the inside only?
Interior caulk and weatherstripping help a lot with drafts, but the outside seal also keeps rain out. If the exterior caulk is cracked, it’s worth fixing, safely, to prevent water damage.
Does window film really help?
Yes, on single-pane or very drafty windows it creates an insulating air gap and stops leaks around the sash. It’s a good temporary fix for the cold season, though it prevents you opening the window.
When should I replace the window instead?
If the frame is rotten, the glass is fogged between panes, or the window no longer closes properly even after adjustment, replacement is usually better than sealing.
This guide is general information, not professional advice. Homes differ, so follow your product manuals and local codes. If anything looks different from what's described, or you feel unsure, stop and call a qualified professional. In an emergency, leave the area and call your local emergency number.
Related guides
Torn window screen
Safe to DIYYes, patching and rescreening is safe work done on a table. The main risk is falling while removing screens from upper-floor windows, so take them out from inside where possible and leave hard-to-reach ones to a professional.
Sliding door hard to open
Safe to DIYCleaning the track and adjusting rollers is safe and easy. Removing a glass panel is a two-person job because panels are heavy and can tip. Never try to handle a cracked or broken tempered glass panel yourself.
Peeling paint
DIY with precautionsYes, most peeling paint is a safe DIY fix, but in homes built before 1978 (US) or older homes elsewhere the paint may contain lead. Test before you scrape or sand, and never dry-sand paint that might contain lead.
Ceiling water stain
DIY with precautionsCovering a dry, stable stain is a safe DIY job. Finding the leak is the real work, and a sagging, bulging or dripping ceiling is a stop sign: keep people away and get help, because wet ceiling boards can collapse.